This invention relates to scanning micropatterns on an optical medium.
Optical media, such as a CDs (xe2x80x9cCompact Disksxe2x80x9d), include data in a pattern (such as a spiral) that is roughly two to five inches in diameter. In digital linear tape (xe2x80x9cDLTxe2x80x9d) systems, long parallel tracks are conventionally formed on the media. Patterns of this size are fairly susceptible to optical scanning errors. For example, deviations in an optical beam caused, e.g., by a sudden jolt to the medium, can result in relatively significant scanning errors, particularly if the optical beam remains off track for a long period of time.
Land and groove patterns, which are used to keep the optical beam on track, can have an adverse affect on reading and writing data on the optical medium. For example, ragged edges on the land and grooves can contribute to noise in the data. Moreover, including land and groove patterns on the media complicates the optical medium manufacturing process.
In general, in one aspect, the invention features an optical medium that includes a micropattern of data. The optical medium has a dimension along which the optical medium is moved, and the micropattern extends along less than this dimension. Formatting data in a micropattern of this size can reduce scanning errors.
More specifically, the time it takes to scan a micropattern is less than the time it takes to scan a regular spiral (since the micropattern extends along less than the dimension of movement of the optical medium). As a result, scanning errors can be substantially confined to the micropattern, without propagating through the rest of the optical medium. Even in cases where jolts or other unwanted accelerations occur to the medium, resulting scanning errors are less severe, since the time over which the jolts or accelerations have an effect is substantially limited to the scanning time of the micropattern.
The micropattern may be formed on an area of the optical medium that does not include land and groove patterns. As a result, noise in the data resulting from the land and groove patterns can be eliminated, and the optical medium can be manufactured with less time and expense.
The foregoing aspect may also include one or more of the following features/functions. The optical medium may include plural micropatterns of data. The plural micropatterns may be arranged in a hexagonal grid pattern. A guard zone may be located between the micropattern and another micropattern on the optical medium. The guard zone comprises an area of the optical medium which does not include data. The guard zone may be 20% or less of the total area of the optical medium.
The micropattern may comprise a microspiral that can be traced from its inner diameter to its outer diameter without leaving the surface of the optical medium. Alternatively, the micropattern may comprise substantially concentric shapes, such as circles. The micropattern may be less than 2 mils in diameter and/or less than 4/106 in2 in area. The optical medium may comprise one of a CD-ROM, digital linear tape, and a card storage medium.
In general, in another aspect, the invention features an optical positioning circuit that includes an electro-optic positioner which scans an optical beam along an optical medium for reading or writing a pattern of data on the optical medium. A driver circuit, such as an inductive-capacitive circuit, drives the electro-optic positioner. Using an electro-optic positioner reduces the need for mechanical devices to position the optical beam on the optical medium, thereby reducing positioning errors associated with such devices.
This aspect of the invention may include one or more of the following features/functions. The electro-optic positioner may comprise a capacitor having a dielectric which deflects light based on an applied voltage signal. The driver circuit may comprise an inductive-capacitive circuit, including an inductive winding of a transformer and one or more capacitors, that operates in a resonant mode to deliver voltage signals to the electro-optic positioner. Operating the inductive-capacitive circuit in resonant mode reduces the input power of the signals needed to drive the electro-optic positioner.
The driver circuit produces the voltage signal that drives the electro-optic positioner. The voltage signal has a substantially sinusoidal waveform with a progressively increasing amplitude and decreasing frequency. Higher frequency portions of the voltage signal control scanning inner diameter portions of the pattern and lower frequency portions of the voltage signal control scanning outer diameter portions of the pattern. A control circuit provides a control signal that causes the electro-optic positioner to position the optical beam at a location to begin forming a new pattern, such as its center.
In general, in another aspect, the invention features a method of scanning a micropattern on an optical medium. The micropattern extends along less than a dimension along which the optical medium is moved. The method includes positioning an optical beam at a location on the optical medium relative to the micropattern, and scanning the micropattern with the optical beam in accordance with a voltage signal.
Other advantages and features will become apparent from the following description and the claims.